Start UTHelper.exe
1. Click on [Load Package] -> Click on the file with the same name as the "Target GPK" .gpk
2. Click on the tab on the left side, Click on [Exports]
3. Look for the file with the same name as the mod and Right-Click on it and choose [Import]
3. Choose the DDS file inside the mod folder.
4. Click on [Save Package]
5. Done

You can create a folder for your mod files:
1. Go to Art_Data\Packages\CH folder
2. Create a new folder
3. Rename it _PC
4. Copy/Paste the modded GPK into your new _PC folder.